make actively playing text editable (#24)

Fixes #5

Enhancements for real time workflows

    Allow editing text while audio is playing. Highlights should now show correctly, and when the track reaches the updated text, it should read the new text
    Show a "playing" icon in the tab that has audio playing

Significant refactor to better support updates of text:

    Split apart (the badly named) PewPewQueue into TrackLoader and TrackSwitcher. TrackLoader is a fancy audio cache with background audio loading features. This makes the TrackSwitchers job easier. TrackSwitcher is mostly just the exact PewPewQueue, but without its complicated internal background queue.

.eslintrc

@@ -6,7 +6,7 @@
   "extends": [
     "eslint:recommended",
     "plugin:@typescript-eslint/eslint-recommended",
-    "plugin:@typescript-eslint/recommended"
+    "plugin:@typescript-eslint/recommended",
   ],
   "parserOptions": {
     "sourceType": "module"
@@ -15,7 +15,14 @@
     "no-unused-vars": "off",
     "no-constant-condition": "off",
     "no-prototype-builtins": "off",
-    "@typescript-eslint/no-unused-vars": ["error", { "args": "none" }],
+    "@typescript-eslint/no-unused-vars": [
+      "error",
+      {
+        "args": "none",
+        "destructuredArrayIgnorePattern": "^_",
+        "varsIgnorePattern": "^_"
+      }
+    ],
     "@typescript-eslint/ban-ts-comment": "off",
     "@typescript-eslint/no-empty-function": "off"
   }